First, second, third, and fourth lenses (in order from an object side) are arranged between the object and an image sensor where an image of the object is formed. The first lens may have a positive refractive power and may be a meniscus lens that is convex toward the object. The second lens may have a positive refractive power and may be a meniscus lens that is convex toward the image sensor. The third lens may have a positive refractive power and may be a meniscus lens that is convex toward the image sensor. At least one of an incident surface and an exit surface of the fourth lens may be an aspherical surface. The fourth lens may have a negative refractive power or a positive refractive power. A viewing angle θ of the lens optical system may satisfy a conditional expression, 2.5